instructions to build locally

### Comment:

For OSX, from xhochy:

(Note this deletes `~/.condarc`)

```
% cat nightly.sh build-logged.sh
#!/bin/bash

set -e

arch -x86_64 bash ./build-logged.sh osx_64_numpy1.18python3.7.____cpython
arch -x86_64 bash ./build-logged.sh osx_64_numpy1.18python3.8.____cpython
arch -x86_64 bash ./build-logged.sh osx_64_numpy1.19python3.9.____cpython
arch -x86_64 bash ./build-logged.sh osx_64_numpy1.21python3.10.____cpython
bash ./build-logged.sh osx_arm64_numpy1.19python3.8.____cpython
bash ./build-logged.sh osx_arm64_numpy1.19python3.9.____cpython
bash ./build-logged.sh osx_arm64_numpy1.21python3.10.____cpython
#!/bin/bash

set -exuo pipefail

VARIANT=$1

gh repo clone conda-forge/tensorflow-feedstock tensorflow-feedstock-${VARIANT}
pushd tensorflow-feedstock-${VARIANT}
gh pr checkout 189
rm -f ~/.condarc
OSX_SDK_DIR=/opt ./build-locally.py ${VARIANT} 2>&1 | tee ${VARIANT}.log
gh gist create ${VARIANT}.log

```

For Linux, from hmaarrfk:

```
#!/usr/env/bin bash

set -ex

docker system prune --force
configs=$(find .ci_support/ -type f -name 'linux_64_*' -printf "%p ")

# Assuming a powerful enough machine with many cores
# 10 seems to be a good point where things don't run out of RAM too much.
export CPU_COUNT=10

mkdir -p build_artifacts

for config_filename in $configs; do
filename=$(basename ${config_filename})
config=${filename%.*}
if [ -f build_artifacts/conda-forge-build-done-${config} ]; then
echo skipped $config
continue
fi

python build-locally.py $config | tee build_artifacts/${config}-log.txt

if [ ! -f build_artifacts/conda-forge-build-done-${config} ]; then
echo "it seems there was a build failure. I'm going to stop now."
echo The failure seems to have originated from
echo ${config}
exit 1
fi
# docker images get quite big clean them up after each build to save your disk....
docker system prune --force
done

zip build_artifacts/log_files.zip build_artifacts/*-log.txt
```